1. Field of the Invention
The current invention relates to an apparatus employed to seal off the interior of tubular members such as a cylindrical pipe or coupling. This relates to an apparatus which in one application is employed to seal off a particular section of pipe by using two of these such devices spaced apart and filling the annular space created between them with a liquid or gas under high pressure in order to check the strength of the pipe's outer wall. In another application these "packers" are used to seal off the inside diameter (I.D.) of a pipe and the inside diameter of a coupling that is screwed onto that pipe, thus creating an annulus between them which includes the "made up" connection. Fluid is then injected into this annulus to test the integrity of the connection between the male threads on the pipe and the female threads on the coupling.
2. General Background
In the oil and gas production industry tubing sections of threaded pipe are joined end-to-end, i.e. pin to box end, to convey fluids. It is desirable that the joints be strong and of tight fit and that the body wall be strong enough to withstand relatively high internal pressures. It is common practice in the oil and gas industry to plug off the ends of each particular joint by screwing test plugs onto the respective threaded ends and to fill the inside of the pipe with a fluid under high pressure to check for leaks behind the collar. Evidence of any leaks when pressured up to a standardized test pressure is an indication that either the external threads on the pin end or the internal threads on the coupling were improperly machined and thus not mating properly, or that they may not have been screwed together with adequate torque or that the body wall was of insufficient strength to withstand the pressure. This test procedure is followed to simulate "down hole" conditions when there is pressure exerted on the connections.
This procedure is very inefficient due to the need to fill up the entire inside of the full length of the tubing with fluid. Often the same pipe is pressure tested several times at the mill, at the threading facility and in the storage yard. After the full length of the body has been tested at the mill, subsequent tests are only necessary to check the integrity of the threaded connections or the coupling connection. Full length pressure testing with screw and plugs is inefficient, time consuming and very dangerous due to the large volume of water combined with the high test pressures. Test plugs sometimes blow out causing great physical damage to equipment and personnel. There is also potential gauling damage to the threads on the pipe which are screwed into the mated test plugs.
The apparatus of the present invention is used to perform a similar pressure test on the pipe threads, but due to the isolation of the annular space to the connection area has radically reduced the volume and surface area that is exerted upon the plug. The innovation of design of the present invention has eliminated the safety hazard of conventional pressure testing and at the same time streamlined the efficiency of the testing procedure requiring only small volume, high pressure pumps and only small quantities of test fluid. Resulting equipment needed to operate these plugs is a small fraction of the size, weight, and cost of those types of pumping, power and water storage units associated with conventional pressure testing.
The apparatus of the present invention is also used to test the made up connections on tubing strings as they are being assembled at the rig site. As each joint is screwed to the one below it on the rig floor, the apparatus of the present invention is inserted into the pipe and set in such a manner that one of the plugs is directly below each threaded connection and the other plug is directly above the connection. The annulus created between these two plugs or packers is then filled and pressured with a fluid to test the integrity of the made up connection. Due to simplified design of the apparatus of the present invention and the reduced volume of test fluid needed to fill the contained annulus, it is possible to operate this equipment with pumps that are a fraction of the size used with conventional methods.